German published patent application DE-OS 27 27 274 discloses a membrane arrangement with a valve needle which is liftable from a valve seat and which admits incoming air as required in order to achieve a change of the air/fuel ratio for the mixture whereby it is intended to attenuate pulsations in the intake line. For handheld power tools and similar apparatus, a low overall weight is strived for in order to make the apparatus simple and easy to manipulate without exerting too great a manual effort. The object of making the chain saw as light as possible can affect the stability of the drive at increasingly higher rotational speeds.